1. Field of the Invention
The present invention relates to fluid pressure sensors. More particularly, the invention relates to a ceramic pressure sensor having a diaphragm to be distorted by pressure so that the pressure of interest can be measured on the basis of the resulting distortion of the diaphragm.
2. Discussion of the Related Art
A conventional pressure sensor, as described in Japanese Patent Unexamined Publication No. Sho. 63-292032, has a diaphragm which is distorted when the pressure to be measured is applied to one side of the diaphragm. The amount of the resulting distortion is measured with a Wheatstone bridge. As shown schematically in FIG. 10, the structure of such a pressure sensor includes a housing a having a threaded coupling portion b with an axial bore c open at its lower end to fluid pressure and an upper mounting counterbore d; a sintered ceramic member e having a diaphragm g on a support h, the diaphragm g being provided within the mounting counterbore d as an integral unit adjacent to a circular gap f that communicates with the fluid pressure introduced to the bore a lid j fitted over the housing a to form a reference pressure compartment k extending between the underside of the lid j and the diaphragm g; resistors i of a Wheatstone bridge formed on the diaphragm g within the pressure compartment k; lead wires m electrically connected to the resistors i; and a clamping member n that secures the lid j to the housing a.
In the pressure sensor having the construction described above, the gas under pressure to be measured is introduced into the circular gap f through the bore c. If the support h and the diaphragm q are exposed to different temperature conditions, the difference in temperature will result in a thermal expansion mismatch between the support h and the diaphragm causing the diaphragm g to distort. Such distortion in the diaphragm g can result in erroneous detection of fluid pressure changes which do not exist in fluid introduced to the bore c.
A further problem is created by the direct connection of the lead wires m to the diaphragm g to be distorted. Thus, the wire connections tend to break on account of extensive vibrations of the diaphragm g. In addition, the lead wires m exert a sufficient load to damp the distortion that would otherwise develop in the diaphragm g.
The pressure sensor shown in FIG. 10 has the additional problem in that the pressure compartment k must be sealed. Because the pressure compartment k is formed by the lid j which is a physically separate member from the housing a, creating and maintaining a sealed compartment can be difficult. If the seal is not sufficiently maintained, it is difficult to maintain a vacuum within the pressure compartment k, if such a vacuum is desired.